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We have recently shown that deletion of constitutively expressed CYP1B1 is associated with attenuation of retinal endothelial cell (EC) capillaiy morphogenesis (CM) in vitro and angiogenesis in vivo. This was largely caused by increased intracellular oxidative stress and increased production of thrombospondin-2, an endogenous inhibitor of angiogenesis. Here, we demonstrate that endothelium nitric oxide synthase (eNOS) expression is dramatically decreased in the ECs prepared from retina, lung, heart, and aorta of CYP1B1-deficient (CYP1B1-/-) mice compared with wild-type (CYP1B1+/+) mice. The eNOS expression was also decreased in retinal vasculature of CYP1B1-/- mice. Inhibition of eNOS activity in cultured CYP1B1+/+ retinal ECs blocked CM and was concomitant with increased oxidative stress, like in CYP1B1+/+ retinal ECs. In addition, expression of eNOS in CYP1B1-/- retinal ECs or their incubation with a nitric oxide (NO) donor enhanced NO levels, lowered oxidative stress, and improved cell migration and CM. Inhibition of CYP1B1 activity in the CYP1Bl-/- retinal ECs resulted in reduced NO levels and attenuation of CM. In contrast, expression of CYPIB1 increased NO levels and enhanced CM of CYP1B1-/- retinal ECs. Furthermore, attenuation of CYP1B1 expression with small interfering RNA proportionally lowered eNOS expression and NO levels in wild-type cells. Together, our results link CYP1B1 metabolism in retinal ECs with sustained eNOS activity and NO synthesis and/or bioavailability and low oxidative stress and thrombospondin-2 expression. Thus CYPIBI and eNOS cooperate in different ways to lower oxidative stress and thereby to promote CM in vitro and angiogenesis in vivo. [ABSTRACT FROM AUTHOR]

The effect of calcium ions on steroid-induced difference spectra of cytochrome P-450, and on pregnenolone formation, has been studied in rat adrenal mitochondria. In the presence of phosphate, addition of calcium chloride to suspensions of these mitochondria resulted in an increase in the inverted type-I difference spectrum induced by pregnenolone or methylandrostenediol and a disappearance of the type I spectrum induced by 25-hydroxycholesterol. The difference in the inverted type I spectrum between mitochondria from ether-stressed animals and those given cycloheximide was abolished. Cholesterol side-chain cleavage was increased, providing an NADPH generator was used as source of reducing equivalents. The difference in side-chain cleavage activity between mitochondria from ether-stressed animals and those given cycloheximide, was maintained. In the absence of phosphate, addition of calcium chloride again resulted in a loss of the type I difference spectrum induced by 25-hydroxycholesterol, but this time there was almost no change in the inverted type I spectrum induced by pregnenolone in mitochondria from rats subjected to ether anaesthesia, and the change in cycloheximide-treated rats was only about 50% of the change in the 25-hydroxycholesterol-induced difference spectrum. These observations are interpreted in terms of interconversions of the various forms of cytochrome P-450 associated with side-chain cleavage proposed to exist in intact adrenal mitochondria. Factors such as bovine serum albumin and EDTA, which increase respiratory control in these mitochondria, also stimulate cholesterol side-chain cleavage activity, as do magnesium ions, but without altering the magnitude of the steroid-binding spectra.